After facing strong opposition to the policy change from flight attendants and its own air marshals, the agency said Monday it was delaying the policy change so that the airline industry, passenger advocates and law-enforcement experts could weigh in on what should be allowed on planes.

"This timing will enable TSA to incorporate the feedback about the changes to the Prohibited Items List and continue workforce training," the TSA said in a statement.

The TSA had planned to let the knives, with blades up to 2.36 inches, on flights starting Thursday. It would have been the first time they would have been back on passenger planes since Sept. 11, 2001, when terrorists armed with box cutters hijacked four jetliners.

TSA chief John Pistole had made the policy change March 5, saying that airport security screeners needed to concentrate on greater risks to air travel.

He also said the change would better match international policy and that other potential weapons, such as scissors and knitting needles, have been allowed on planes since 2005.

The Flight Attendants Union Coalition, which represents 90,000 flight attendants and lobbied against the policy change, welcomed the postponement. The group argued that if TSA wants to change the policy, the agency must go through a formal rulemaking process.

"In the wake of the terrorist bombing in Boston last week ... now is not the time to weaken transportation security," said Sara Nelson, international vice president of the Association of Flight Attendants. "Flight attendants are breathing a sigh of relief that the weapons that led to the deadliest attack on U.S. soil in our nation's history will not be allowed in the aircraft cabin this week."